Hyper-saline produced water treatment for beneficial use

Producing oil and gas is always accompanied with large amounts of effluent water, called “produced water” (PW). These huge quantities of water can be used (if treated efficiently and economically) for many useful purposes like industrial applications, irrigation, cattle and animal consumption, and domestic water use for washing, air-cooling, gardening, and even for drinking. Besides the oil constituents, one of the most important concerns of PW is its high salinity. The salt content of the PW in the south of Iraq (the study area) reaches elevated levels of more than 240 g/L. Desalination of such hyper-saline water is considered as extraordinarily expensive because of large energy requirements. In this thesis, a hybrid process consisting of forward osmosis (FO) and membrane distillation (MD) processes is proposed as a treatment method for hyper-saline oilfield produced water. In the FO-MD concept, FO acts as a pre-treatment step to protect the MD membrane from the fouling materials that cause pore wetting while MD works as a recovery method for the FO draw solution. The FO-MD combination might be more cost effective for PW treatment if waste or low-grade heat is available nearby the oil extraction facilities. The performance of the FO-MD process was evaluated using four different draw solutions (i.e. NaCl, KCl, MgCl2 and LiCl) and commercially available membranes (HTI-TFC membrane for FO and 3M-PP membrane for MD). There was a substantial difference between the FO and the MD water flux for the tested draw solutions and this difference was attributed to the difference in osmotic pressures and vapor pressures of these draw solutions respectively. The 4.8 M MgCl2 draw solutions showed the best performance with stable fluxes for both FO and MD. The FO-MD process showed 100 % rejection of oil and salts and no change in conductivity of permeate was observed during the 20 hr. of operation, hence showing excellent desalination performance.